.\" -*- nroff -*-
.\" Copyright 2010 Cisco Systems, Inc.  All rights reserved.
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.\" $COPYRIGHT$
.TH MPI_Comm_test_inter 3 "Jun 10, 2020" "4.0.4" "Open MPI"
.SH NAME
\fBMPI_Comm_test_inter \fP \- Tests to see if a comm is an intercommunicator.

.SH SYNTAX
.ft R
.SH C Syntax
.nf
#include <mpi.h>
int MPI_Comm_test_inter(MPI_Comm \fIcomm\fP, int\fI *flag\fP)

.fi
.SH INPUT PARAMETER
.ft R
.TP 1i
comm
Communicator (handle).

.SH OUTPUT PARAMETERS
.ft R
.TP 1i
flag     (Logical.)
.ft R
.TP 1i
IERROR
Fortran only: Error status (integer).

.SH DESCRIPTION
.ft R
This local routine allows the calling process to determine the type of a communicator. It returns true for an intercommunicator, false for an intracommunicator.
.sp
The type of communicator also affects the value returned by three other functions.  When dealing with an intracommunicator (enables communication within a single group), the functions listed below return the expected values, group size, group, and rank.  When dealing with an inter-communicator, however, they return the following values:
.sp
.nf
MPI_Comm_size	Returns the size of the local group.
MPI_Comm_group	Returns the local group.
MPI_Comm_rank	Returns the rank in the local group.
.fi
.sp
To return the remote group and remote group size of an inter-communicator, use the MPI_Comm_remote_group and MPI_Comm_remote_size functions.
.sp
The operation MPI_Comm_compare is valid for intercommunicators. Both communicators must be either intra- or intercommunicators, or else MPI_UNEQUAL results. Both corresponding local and remote groups must compare correctly to get the results MPI_CONGRUENT and MPI_SIMILAR. In particular, it is possible for MPI_SIMILAR to result because either the local or remote groups were similar but not identical.
.sp
The following accessors provide consistent access to the remote group of an
intercommunicator: MPI_Comm_remote_size, MPI_Comm_remote_group.
.sp
The intercommunicator accessors (MPI_Comm_test_inter, MPI_Comm_remote_size, MPI_Comm_remote_group) are all local operations.

.SH ERRORS
Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ functions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI::Exception object.
.sp
Before the error value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job, except for I/O function errors. The error handler may be changed with MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.

.SH SEE ALSO
.ft R
.sp
.nf
MPI_Comm_remote_group
MPI_Comm_remote_size
MPI_Intercomm_create
MPI_Intercomm_merge

